Air-to-air vs. air-to-water heat pump KFW55 house - cooling function important

We don't find shading that bad now, we are already doing it completely in our apartment. This currently keeps the temperature at 25° in our KFW55 apartment. The problem here is more the oven and dryer, as they naturally release a bit more heat energy into the apartment each time. In the house, we even have the advantage that there are always 1–2 directions where you don't have to shade. So that shouldn't be a problem. Without it, the underfloor cooling probably doesn't make much sense either if it only changes the temperature by 2-3°. But being able to cool down from 25° to 22° would be really nice, and it's certainly better than no cooling at all. Unfortunately, the budget for more is not available at the moment.

Have you planned a central ventilation system?
For us, it is now leaning towards an air-water heat pump with central ventilation (still uncertain whether with cooling function) and photovoltaics.

Yes, a central supply and exhaust ventilation system is planned. Photovoltaics are definitely planned for the long term; whether we build them in right from the start simply depends on the total construction costs. If there is still room in the budget, we would include photovoltaics directly, otherwise retrofit them later.

Our situation is somewhat special due to home office – but in summer with 2 running computers and 4 monitors, we quickly get >30°C in the office without cooling. The rest of the house also heats up strongly through the window surfaces, despite good insulation.

These are also our concerns. We both work as programmers, often from home, and stereotypically also spend a lot of our free time on the PC. Even in our very cold old building apartment you can already tell what a difference it makes – quite pleasant in winter, but noticeably warmer in summer. I can hardly imagine what it would be like in a well-insulated house. 2-3° cooling through underfloor heating then seemed rather useless in proportion, even if it certainly helps a bit.

On the other hand, unfortunately, it is as jrth2151 says:

If we had unlimited money available, we would have gone directly for photovoltaics + air conditioning.

Costs are unfortunately a factor as well. In the end, we will probably have to bite one of the bitter pills – spend more money on a proper air conditioning system, or take the risk that the cooling function of underfloor heating will not be sufficient. From the answers here in the thread, we are at least more certain that it will probably be an air-water heat pump, and not an air-air heat pump.

You often read the opinion here that you have to consistently close all shutters in summer. I partly understand that - without shading it's hardly possible in a new building. But really closing EVERYTHING, the whole summer? Then you sit like a hobbit in the cave. For me, quality of living looks different.

It's enough if you shade the sunny side. With clever planning, it doesn't necessarily have to get dark. We have good 10 meters of floor-to-ceiling windows in the open space, but one facing east, two facing south, one facing west. That way we can shade all around without it feeling dark. Almost every room has windows in two directions. It doesn't work quite as well as in the open space, but still quite well. We have the bedrooms facing south. That just happened, but it has the advantage that shading there during the day doesn’t really bother us. The study is in the northwest, so I can get by there quite long without shading. The concrete ceilings absorb quite a bit of heat during the day and at night we ventilate it out again. The hard test with a week of muggy 35 degrees is still pending, but I am quite confident, despite the EH40 building envelope and large windows.
But I also know it differently, for example from the office. There you really sit in the cave from lunch time onwards. And the window areas are huge, but the openable window is more like a loophole. So you don't get rid of the heat in the morning by ventilating. Several powerful computers and people in one room are also a problem. 100W per person, 300W per computer, plus the peripherals... that quickly adds up to 1 kW heating power in the room.

The cooling function of the heat pump, on the other hand, costs only around €500 extra, so at first only that would be an option.

At €500 I would take it and then see how much you need it. For us, €4k was quoted, that was too much for me.

From real practice and operation over several years: The underfloor heating-cooling simply works. I am absolutely glad that I insisted on it, and my wife regularly thanks me for it in the summer. Yes, exactly, the woman who hates nothing more than cold feet. Do it or don't, I don't care, I don't make any money from it. Only when I hear "it doesn't help anyway" I have to say: Oh yes, it does.

Regarding shading. Well, you just do what you can. The two children's rooms have large south-facing windows – in the morning, when the kids are out of the house, we just lower the blinds. The stuffed animals are then in the dark. Yes, the roof window in the guest bathroom is also covered by a blind. It bothers me very little. I built the ground floor south side so that in summer no sunlight shines directly on the doors, so the blinds stay up and it is brighter than you would wish.

In short: Underfloor heating-cooling works wonderfully – within the limits the system obviously has. I have 22.0°C inside constantly with 34.5°C outside, and that is exactly what I want. Shading does NOT mean living in darkness.

At 500€ I would take them and then see how many you need. With us, they asked for 4k for it, which was too much for me.

I agree. For us, it was 2k and we preferred the proper air conditioning.

These are also our concerns. We both work as programmers, often from home office, and stereotypically also spend a lot of our free time at the PC.

Are you "we"? :D No, no joke – it’s the same with us. Both in IT, both full remote, and also rather gaming than watching TV in our free time. Don’t underestimate the heat generation in a new build. We already had that for 2 years in our first house. KfW55, the office was even so hot in winter that we had to ventilate constantly there, or, if it was noisy outside, sometimes run the AC. In December. o_O In summer you’d die without AC. Above all, though, working in a well-tempered room is much more comfortable. The price of AC strongly depends on how large you dimension it. In the first house, we had a smaller outdoor unit and 3 split units. One for the entire upper floor, one for the office, and one for living/cooking. That was completely sufficient for the house size (about 150m²). For that, we paid about 5k directly through the financing back then. The new house is somewhat larger. We also took a nasty hit to the wallet when the plumber said we’re looking at about 14k. o_O But we’ve already invested part of the buffer there. I’d say – we will hit the 1.5° target if nothing world-shaking happens. And it won’t get any cooler. I don’t know how it is with you, but for us spring has basically failed already again this year. We heated until May (currently in old building, to be clear), and were able to set up the mobile AC unit in the office again just under 2 weeks later. Accordingly, the investment in AC was worth it for us because I believe we will need it often in the future. For that, we save elsewhere where it’s purely about optics. I hope I’ll find my metal railing less annoying when I sweat less in August.

Even in our very cold old building apartment, you can already feel the difference – quite pleasant in winter, in summer it makes the room noticeably hotter. I almost don’t want to imagine how that works in a well-insulated house. 2-3° cooling through underfloor heating then appeared rather useless comparatively, even if it certainly helps a bit.

You pretty much assess that correctly. I currently live temporarily (because the construction is not finished yet) in an old house, very poorly insulated. Office under the roof, and it’s been almost unbearably hot in there all June. The rest of the house is still okay. Before that I lived for 2 years in an insulated new build, and back then we already had the problem end of May: Outside it was a pleasant 20°C, inside 28. We didn’t have on our radar back then that we’d have to shade. You don’t need much heat outside, the light coming through the window areas alone suffices. You can hardly get the heat out of the house again.

But I also know it differently, for example from the office. There you really sat in a cave after lunch break. And the window areas are huge, but the window that can be opened is more like a loophole. So you can’t ventilate the heat out in the morning. Several stronger computers and people in a room are also a problem. 100W per person, 300W per computer, plus the peripherals... you quickly get to a kW heating power in the room.

That’s reality at home for us too. The office is not as big as a company office, there are two of us, and a lot of hardware is running. I don’t even know if the 300W is enough for our computers.